overview of heavy-ion fusion focus on computer simulation aspect*

The Heavy Ion Fusion Virtual National Laboratory

Overview of Heavy-Ion FusionFocus on computer simulation aspect*

Computer Engineering Science seminar

University of California at Berkeley

May 4, 2004

Jean-Luc Vay(and many others from the)

Heavy-Ion Fusion Virtual National Laboratory

Lawrence Berkeley National Laboratory

*This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Berkeley and Lawrence Livermore National Laboratories under Contract Numbers DE-AC03-76SF00098 and W-7405-

Eng-48, and by the Princeton Plasma Physics Laboratory under Contract Number DE-AC02-76CH03073


The U.S. Heavy Ion Fusion Program - Participation

Lawrence Berkeley National Laboratory MITLawrence Livermore National Laboratory Advanced CeramicsPrinceton Plasma Physics Laboratory Allied SignalNaval Research Laboratory National ArnoldLos Alamos National Laboratory HitachiSandia National Laboratory Mission ResearchUniversity of Maryland Georgia TechUniversity of Missouri General AtomicStanford Linear Accelerator Center MRTI Advanced Magnet Laboratory Idaho National Environmental and Engineering Lab University of California

a. Berkeley b. Los Angeles c. San Diego

Employees of LBNL, LLNL, and PPPL form the U.S. Virtual National Laboratory for Heavy Ion Fusion


Outline

Fusion energy– Principles, advantages/disadvantages– Basic requirements– Paths to fusion

Heavy Ion Inertial Fusion– The target– The chamber– The accelerator– The source

Modeling developments– New physics– New algorithms– Experiment/simulation interface– Data analysis

Conclusion


FUSION ENERGY


FUSION ENERGY: principles


Equivalence of mass and energy

Einstein’s equation

– m = mass of particle– c = speed of light ~ 3.108 m/sec

huge amount of energy can be extracted from mass conversion.

2mcE

Example:

if a 1 gram raisin was converted completely into energyE = 1 gram x c2

= (10-3kg) x (3.108 m/sec)2

= 9.1013 Joules

~ 10,000 tons of TNT!


Advantages of fusion

Virtually inexhaustible resources of fuel (water)

Clean (no CO2 emission, almost no radioactive waste)

Fusion reactors are inherently safe. They cannot explode or overheat.

Byproducts or fuel cannot be used to build weapons of mass destruction

The fuel is accessible worldwide

Disadvantages of fusionComplex, still at conceptual stage

Centralization of power sources


FUSION ENERGY: Basic requirements


Two fundamental forces at play

Holds

Holds


In order to fuse, the nuclei have to

overcome electrostatic barrier: go into the right direction:

-50 -40 -30 -20 -10 0 10 20 30 40 50

-0.4

-0.2

0.0

0.2

0.4 electric strong sum

Pot

entia

l (ar

bitr

ary

units

)

distance (arbitrary units)

D

T

D

out

out

In

T

out

Slice view 3D view

need energy (millions of degrees) need many events (many particles)

Find these conditions in?Find these conditions in “PLASMAS”


States of matter


FUSION ENERGY: Paths


The different paths to fusion energy

Tokamaks ITER

Lasers (NIF)

Particle accelerators

“God’s way”“Human ways”


HEAVY ION INERTIAL FUSION


An Artist’s Conception of a Heavy Ion Fusion Power Plant

From the overall system, we identify several parts and study them separately using theory, experiments and computer simulations.


HEAVY ION INERTIAL FUSION: the target


For symmetric illumination, the target is enclosed into a capsule

Examples of capsule

Hydrodynamic simulation of target implosion and capsule expansion (Lasnex)

“hybrid”“close coupled”


LASNEX is validated against Laser fusion experiments


HEAVY ION INERTIAL FUSION: the chamber


Inside the chamber

(Lasnex simulation)

(Tsunami simulation)


Cut-away view shows beam and target injection paths for an example thick-liquid chamber


beam ions Flibe ions electrons

target

3-D BPIC simulation of beam propagating through Flibe

at 27.6 ns; 10 GeV, 210 AMU, 3.125 kA, 5x1013/cm3 BeF2


Does plasma neutralization really work?

LSP simulations results for standard bismuth main pulse

1.2-mm waist is acceptable for distributed-radiator target

:

-4 -2 0 2 4y (mm) [simulation]y (mm) [simulation]

-4 -2 0 2 4

y (mm) [experiment] y (mm) [experiment]

0

2

4

6

8 -4 -2 0 2 4

simulation experiment

simulation

experiment

-4 -2 0 2 4

Unneutralized beam Partially neutralized beam

Inte

nsi

ty i

n f

oca

l p

lan

e

400µA, 160 keV, Cs+

Electrostatic quadrupole lenses for beam set-up

Magnetic quadrupoles

for final focusing

Final-Focus Scaled Experiment studied effect of neutralizing electrons (from a hot filament) on focal spot size

LSP particle-in-cell


HEAVY ION INERTIAL FUSION: the accelerator


Principles of particle acceleratorAcceleration Transverse confinement (magnetic or electric)

(SLAC)


High Current Experiment (HCX) began operation January 11, 2002.

10 ES quads

ESQ injector

Marx

matching

diagnostics

diagnostics

High-Current Experiment (HCX): first transport experiment using a driver-scale heavy-ion beam

K+, 1 - 1.8 MeV, 0.2 - 0.6 A, 4 - 10 µs, 10 ES quads, 4 EM quads

HCX is to address four principal issues: – Aperture limits (“fill factor”)? – How maximum transportable current affected by misalignment, beam

manipulations, and field nonlinearities?– beam halo?– effects of gas and stray electrons?

9.44 m

2.51 m 3.11 m 2.22 m 1.38 m

ESQ injector Matching section 10 ES quadsend stationdiagnostics

K+ source


3-D WARP simulation of HCX injector


HEAVY ION INERTIAL FUSION: the source


4 mA/cm2

100 mA/cm2/beamlet

Two possible ion source approaches

Use a large diameter but low current density single-aperture ion source. (traditional)

Extract hundreds of mm-scale high current density beamlets, from a multiple-aperture ion source. (experimental)


STS-500 investigating large-aperture diode dynamics

ExptWARP

Warp simulation Experimental results

RisetimePhase Space at End of Diode


RZ and transverse slice simulation used to understand parameter space and optimize design

3D used for validation

Physics design with spherical plates completed; iterated with designer to ensure “buildability”

0. 1.5-7.5

7.5

0.5 1.0Z (m)

X (mm)

Current = 0.07 Amps, Final energy = 400 keV

Normalized

emittance

Physics design of 119-beamlet merging experiment on STS500 is complete


Parameters Results Status

Current density 100 mA/cm2 (5 mA) met goal

Emittance Teff < 2 eV met goal

Charge states > 90% in Ar+ met goal

Energy spread < a few % beam suffers CX met goal

Beamlets from Argon RF Plasma Source meet the required specifications

Single Beamlet:

Multiple Beamlet:RF Source: Image on Kapton:


Merging Beamlet fabrication is in progress

Einzel Lens Test

(STS-100)qualified high gradient insulator (up to 35 kV/cm).

Full-gradient test (STS-500)

vacuum gap voltage gradient (>100kV/cm)

Soon


MODELING DEVELOPMENTS


Our next-step vision

Beam Science Inertial Fusion Energy

Brighter sources/

injector ESQ Channel

1.2 MV Preaccelerator using Einzel lens focusing for beamlets

0.4 MV beamlet- merging section

1.0 m

7 cm

Maximum <J >, Bn Transport

Beam neutralization

Theory/simulations

Accelerator

Final Focus

Source and injector

NOW NEXT STEP

integrated beam experiment (IBX)

...to test source-to-target-integrated modeling

3


The IBX mission is to demonstrate integrated source-to-focus physics

7m25 ns

40 m (10 MeV)

15 m250 25 ns

2 m250 ns 1.7 MeV

Ion: K+ (1 beamline)

Total half-lattice periods: 148

Total length: 64 m5 - 10 MeV

Injector

Accelerator

DriftCompression

Final Focus

Neutraliz

ation


We will develop an integrated, detailed, and benchmarked source-to-target beam simulation capability

delta-f, continuum Vlasov, EM PIC

electrostatic / magnetoinductive PIC EM PIC rad -hydroWARP LSP BPIC

BEST SLV LSPdelta-fBEST

Buncher Finalfocus

Chambertransport TargetIon source

& injector Accelerator


MODELING DEVELOPMENTS: new physics


Electron production missing in simulation of HCX

Beam head hit the structure


Toward a self-consistent model of electron effects

Plan for self-consistent electron physics modules for WARP

Key: operational; implemented, testing; partially implemented; offline development

WARP ion PIC, I/O, field solve

fbeam, , geom.

electron dynamics(full orbit; drift)

wall electron source

volumetric (ionization)

electron source

gas module

penetration from walls ambient

charge exch.ioniz.

nb, vb

fb,wall

fb,wall

sinks

ne

ions

Reflectedions

fb,wall


WARP and electron cloud code POSINST merged

• the code POSINST, specialized in the prediction of electron clouds in high energy physics accelerator, was merged with WARP

• brings new capabilities and collaborations for study of electron clouds in heavy ion fusion and high energy density physics

• Specialized GUI page added to WARP GUI by UCB UG student– run POSINST

– Read/plot output data


New large time-step electron mover reproduces the e-cloud calculation in < 1/25 time

Full-orbit , t=.25/fce Large time-step interpolated

A major invention that should have application to many fields including MFE, astrophysics, near-space physics...


MODELING DEVELOPMENTS: new algorithms


challenging because length scales span a wide range: m to km(s)

End-to-end modeling of a Heavy Ion Fusion driver

m

m

km


The Adaptive-Mesh-Refinement (AMR) method

addresses the issue of wide range of space scales

crosscutting example from CFD

AMR concentrates the resolution around the edge which contains the most interesting scientific features.

3D AMR simulation of an explosion (microseconds after ignition)


Particle-In-Cell + AMR applied to HCX source in axisymmetric (r,z) geometry

0.0 0.1 0.2 0.3 0.40.0

0.2

0.4

0.6

0.8

1.0 ngf=1, npf=1 (base grid) ngf=2, npf=4 ngf=4, npf=16 ngf=1, npf=4 (AMR)

4*

no

rma

lize

d R

MS

em

itta

nce

(

mm

.mra

d)

Z(m)

Low res.Medium res.High res.Medium res. + AMR

Z (m)

X (

m)

4 N

RM

S(

mm

.mra

d)

AMR-PIC simulation of ion source

The high res. result is recovered with medium res.+AMR around beam edges at 1/4 of comput. cost


Collaboration HIF/CBP and ANAG (Phil Colella’s group) to provide AMR library of tools to Particle-In-Cell codes

Example of WARP-Chombo injector field calculation


Vlasov Models offer low noise, large dynamic range

x

px 10-5

10-4

10-3

10-2

10-1

1

Solution of Vlasov equation Solution of Vlasov equation on a grid in phase spaceon a grid in phase space

Courtesy E. Sonnendrucker et al., IRMA, U. of Strasbourg with HIF-VNL

Moving mesh Adaptive mesh


MODELING DEVELOPMENTS: interface experiment/simulation

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Nor

mal

ized

X E

mit

tan

ce (

m

m-m

rad

)

20151050

z (m)

self-consistent 2-plane reconstruction after ESQ 3-plane reconstruction after ESQ semigaussian

2.22 m 2.22 m 2.22 m

HCX transport line (10 quads/tank)Matching sectionInjector

2.51 m 3.11 m

We are using simulations to learn what data we need to take, and how best to use the data we obtain

• Simulations initialized using 4D particle distributions synthesized from ESQ-exit slit-scan data (simulated, here) are far better than those using an ideal distribution

• An (x,y) scan, in addition to (x,x) and (y,y), is important

z (m)

No

rmal

ized

x e

mit

tan

ce (-

mm

-mr)

semi-Gaussian

Integrated simulation, starting at source

3-plane synthesisadding (x,y) data

2-plane synthesisusing (x,x) and (y,y)

Optical slit diagnostic is yielding unprecedented information about HCX beam distribution

isosurface where ƒ(x,y,x) = 30% of peak

face-on (xy) view rotated to right

ƒ(y,x) (integ. over x)

line is mean x´(x=0) vs. y

x´

y

shadow of “bridge” across slit

x

u

vy

dzh

• This scanner measures f(x,y,x)• It contains such information as

the (y,y) distribution as a function of x, or averaged over all x

• It can be “gated” in time

Phase-space diagnostics


MODELING DEVELOPMENTS: data analysis


Advanced interactive particle viewer

• High dimensionality (3-D X + 3-D V) data inherently difficult• Collaboration with visualization group for developing new kind of particle viewer

Interactive selection of particles is automatically translated to another view:

A new rendering technique gives compact representation of 6-D data:


CONCLUSION

Fusion is a very attractive source of energy– Would solve many problems– But hard to achieve

Still far: there is lot of exciting science to study and technologies to develop

Computer simulation plays a crucial role in studying science, planning and analyzing experiments

The design of a full scale driver will rely heavily on integrated simulation from end-to-end

In order to reach our goal, we are developing new state-of-the-art algorithms for computation and data analysis

For more, visit our home page at http://hif.lbl.gov


BACKUP slides


3D simulations of IBX

z (m) in fixed-then-moving frame

Beam created at source, matched, accelerated, begins to drift compress.

Parameters:

1.7 6.0 MeV

200 100 ns

0.36 0.68 Amps

4.6 us of beamtime

separatingtail

(C/m)

Mesh frozen

Mesh accelerates with beam

Driftcompression


BASIC PLASMA COMPUTER MODELS


Computer simulation of plasmas

We compute on various platforms: pc (Pentium, Athlon), Pentium clusters, IBM-SP

IBM-SP very powerful parallel computer but need to simulate systems that contains at least 1000 billions of real particles

Even on the NERSC IBM-SP, the simulation of all the real particles is usually unfeasible

We have to make approximations!


Computer simulation of plasma as collection of particles

– We use macroparticles (1 macroparticle = many real particles)– We compute the force (field) on a grid– We advance particle and fields by finite time steps

x

y


Computer simulation of plasma as fluid

– A system containing many particles may (under certain conditions) be modeled as a fluid

Example: air is made of molecules but is often described as a fluid

– Restriction: one location = one velocity

– We compute the fluid equation on a grid

– The temporal evolution of the fluid is computed using finite time steps

x

y

overview of heavy-ion fusion focus on computer simulation aspect*

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